1. Field of the Invention
The present invention relates to an automatic analyzer of blood automatically analyzing blood samples for transfusions, and more particularly to an automatic assay system for screening blood samples to prevent or inhibit the onset of transfusional hepatitis.
2. Description of the Prior Art
The occurrence of transfusion-induced hepatitis is one of the difficult medical problems in recent years. Since this disease is epidemiologically in correlation with blood transfusion, the incidence of the disease tends to increase with the increase in the amount of transfusion due to the advance of surgery. The disease not only retards the recovery of the transfused patient but also produces a prolonged aftereffect on him, possibly enadngering his life, and hence posing a serious problem of the community.
Presently, the Japanese Red Cross Society, Blood Center screens out abnormal blood using alanine aminotransferase (hereinafter referred to as "GPT"), Wasserman reaction and HBs as indicators. In actuality, however, hepatitis postoperatively develops even from normal transfused blood which is up to 35 IU/liter in GPT and negative for the Wasserman reaction and for HBs, and a majority of such cases of hepatitis are of the non-A non-B type. Accordingly, to completely prevent the onset of postoperative hepatitis, natural transfusion blood needs to be replaced by packed blood preparations or artificial blood, but an artificial blood which is comparable to natural blood still remains to be developed as an actual problem. At present, therefore, natural blood is used at some risks, and it is imperative to develop a highly reliable method of screening transfusion blood to avoid the hazard of hepatitis.
In the course of our research on substances which are serviceable as indicators of non-A non-B type hepatitis, we checked a large number of blood samples for serum guanase activity and further statistically investigated the relation between this activity and the incidence of hepatitis to find a very good correlation therebetween. While guanase is an enzyme associated with the metabolism of purine bases, as is well known, the finding is of extreme interest regardless of how the variation in the amount of the enzyme is biochemically related to non-A non-B type hepatitis.
On the other hand, we investigated the possible correlation between the guanase activity and the GPT activity which is usually used for screening normal blood. The investigation revealed little or no correlation between these activities (see FIG. 4). This indicates that the screening of transfusion blood with reference to the guanase activity has an epidemiological significance different from that of the conventional method.
Based on the above findings, we have already filed Published Unexamined Japanese patent application No. 64616/1982, finding that a manual method of assaying guanase by direct colorimetric determination of ammonia is useful especially for screening the blood for transfusions.
Stated more specifically, we checked samples of normal blood obtained from the Japanese Red Cross, Blood Center for guanase activity by the manual method, i.e. by reacting the serum guanase with 8-azaguanine as a substrate and colorimetrically determining the resulting ammonia by the indophenol reaction. The correlation between the guanase activity thus determined and the occurrence of hepatitis after blood transfusion was investigated based on the findings obtained after transfusions at two clinical institutions. Table 1 and Table 2 show the results.
TABLE 1 ______________________________________ Guanase activity (IU/L) &gt;2.6 &lt;2.5 Total ______________________________________ Number of patients 9 13 22 developing hepatitis Number of patients 5 89 94 without hepatitis Total 14 102 116 Incidence of hepatitis (%) 64.3 12.7 ______________________________________ X.sup.2 = 18.6 &gt; (1,0.001) = 10.83 Significant difference at 0.1% level.
TABLE 2 ______________________________________ Guanase activity (IU/L) Unchecked &gt;2.1 &lt;2.0 Total ______________________________________ Number of patients 15 20 15 50 developing hepatitis Number of patients 10 6 36 52 without hepatitis Total 25 26 51 102 Incidence of hepatitis (%) 60 76 29.4 ______________________________________ X.sup.2 = 17.5 &gt; (2,0.001) = 13.82 Significant difference at 0.1% level.
The above tables reveal that the screening of the blood for transfusions according to guanase activity as a standard remarkably reduces the incidence of postoperative hepatitis. We further carried out research and found it most suitable for select blood with guanase activity of less than 2.9 IU/L by the above method.
However, the above screening method, which is practiced manually and requires a period of time for the indophenol reaction, has the drawback of being unable to check a large quantity of blood samples quickly and not amenable to automation. Accordingly it has been desired to provide automatic analysis method and apparatus for assaying and screening a large number of samples continuously and rapidly.
In this respect, various manual methods other than the foregoing are known for determining guanase activity, including some which appear relatively efficient, so that it will be useful to select such a method for automatic analysis. Nevertheless, what matters is whether there is a correlation between the manual method and the feasible automatic analysis method. For example, the manual method resorting to the indophenol reaction differs in substrate from the reaction rate assay or end point assay used for automatic analysis according to the present invention. Additionally, little has been reported as to an automatic assay of guanase activity by any method. It is therefore difficult to definitively conclude that the manual method and the automatic method are alike in the result to be achieved. In fact, it was not clear whether the reference value of 2.9 IU/L for the manual method could be the reference level for screening the blood by automatic analysis.
We have practiced a specific method of determination using a specific automatic analyzer to investigate the correlation between this method and the conventonal manual method and found a very good correlation between the two methods in respect of gunanase activity. We have further found that by this method thus conducted automatically, that blood can be screened rapidly with high reliability when a reference value of about 1.8 IU/L is used under specified conditions instead of the conventional value of 2.9 IU/L.